1. Field of the Invention
The present invention relates to a radiographic image conversion panel including a support and a photostimulable phosphor layer which is formed on the support by a vapor phase deposition method.
2. Description of Related Art
Conventionally, the so-called radiography using a silver salt to obtain radiographic images has been utilized. However, a method for imaging radiographic patterns without using a silver salt have also been developed. That is, a method in which radiation transmitted through a subject is absorbed to a photostimulable phosphor, subsequently the photostimulable phosphor is excited with a certain energy to emit radiation energy accumulated in this photostimulable phosphor, and this fluorescence is detect to create a picture, is known.
As a particular method, a method for radiographic image conversion using a panel where a photostimulable phosphor layer is provided on a support and both or either visible light and infrared ray is used as excitation energy, is disclosed in U.S. Pat. No. 3,859,527.
Recently radiographic image conversion panels using the photostimulable phosphor where Eu is activated on alkali halide such as CsBr as a host have been proposed as means for photographic pattern conversion using a photostimulable phosphor with high luminance, high sensitivity and high sharpness. Particularly, it says that making Eu an activator enables improvement of X-ray conversion efficiency which has been impossible conventionally.
On the other hand, as materials of the support on which such a photostimulable phosphor layer is formed, for example, high molecular resins, ceramics, glasses, metals and the like are used, as shown in the specification of Japanese Patent No. 2899812. The high molecular resins are preferable because they are generally good in workability, radiation absorbability is low and transmittance is high, but on the other hand, mechanical strength is weak and heat resistance is not excellent. The ceramics, glasses and metals are sufficient for heat resistance but have a problem that the sensitivity thereof is lowered in use as the panel because the radiation absorbability is high and transmittance is low. Particularly, the photostimulable phosphor layer described above has been a problem that the production efficiency is lowered when glass is used as the support because the photostimulable phosphor layer is formed on the support by a vapor phase deposition method such as a deposition method and the photostimulable phosphor layer can be vapor-deposited on the glass support only in an very high temperature condition.
The present inventors have found it advantageous for solving the issues described above that carbon fiber reinforced plastic (CFRP) in which heat resistant resin is impregnated in carbon fibers is used as the support.
However, the above support is produced by arranging the carbon fibers in one direction. In the support, a plurality of carbon fiber reinforced plastic sheets in which the heat resistant resin such as epoxy resin is impregnated in carbon fibers are laminated, and these carbon fiber reinforced plastic sheets are cured by applying heat and pressure. Besides, the plurality of carbon fiber reinforced plastic sheets are laminated such that directions of the carbon fibers are aligned in one direction.
Therefore, when the photostimulable phosphor is vapor-deposited on such a support by the vapor deposition method to form the photostimulable phosphor layer, a thermal expansion coefficient of the photostimulable phosphor layer made up of CsBr or the like is large, and furthermore, residual stress at the vapor deposition is left on the support made up of the carbon fiber reinforced plastic sheets. Thus, a trouble occurs that the panel in which the photostimulable phosphor layer is formed on the support warps along the direction of carbon fibers in the support and this has sometimes caused uneven images.